Rev Andal Med Deporte. 2015;8(3):93–102

www.elsev ier .es / ramd

R e v i s t a A n d a l u z a d e

Medicina del Deporte

Original article

Acute effects of two different stretching techniques on isokineticstrength and power

F. Ayala a,b,∗, M. De Ste Croix c, P. Sainz de Barandad, F. Santonja e,f

a Sports Research Centre, Miguel Hernandez University of Elche, Spainb ISEN University Formation, Centre Affiliated to the University of Murcia, Spainc Faculty of Applied Sciences, School of Sport and Exercise, University of Gloucestershire, Gloucester, United Kingdomd Faculty of Sports Sciences, University of Murcia, Spaine Faculty of Medicine, University of Murcia, Spainf Department of Traumatology, V. de la Arrixaca University Hospital, Murcia, Spain

a r t i c l e i n f o

Article history:

Received 16 October 2013

Accepted 26 June 2014

Keywords:

Warm-up

Strength performance

Peak torque

Power output

Isokinetic

a b s t r a c t

Objectives: To examine and compare the acute effects of short duration static and dynamic lower-limb

stretching routines on the knee flexor and extensor peak torque and mean power during maximal con-

centric and eccentric muscle actions.

Method: Forty-nine active adults completed the following intervention protocols on separate days:

non-stretching, static stretching and dynamic stretching. After the stretching or control intervention,

concentric and eccentric isokinetic peak torque and mean power of the leg extensors and flexors were

measured in prone position. Measures were compared via a fully-within-groups factorial ANOVA.

Results: Neither static nor dynamic stretching has influence on isokinetic peak torque and mean power

when they were compared with the control condition. Paired comparison also showed that the isokinetic

strength and power results reported by dynamic stretching session were slightly higher than those found

during the static stretching session.

Conclusions: Short pre-exercise static and dynamic lower-limb stretching routines did not elicit

stretching-induce reductions or improvements in knee flexor and knee extensor isokinetic concentric

and eccentric strength. In addition, the findings of the current study support the claim that dynamic

stretching may be preferable to static stretching as part of a warm-up designed to prepare for physical

activity.© 2015 Consejería de Educación, Cultura y Deporte de la Junta de Andalucía. Published by Elsevier

España, S.L.U. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Efecto agudo de 2 técnicas de estiramiento diferentes sobre la fuerza y potenciaisocinética

Palabras clave:

Calentamiento

Fuerza muscular

Pico de fuerza

Potencia

Isocinético

r e s u m e n

Objetivos: Examinar y comparar los efectos agudos de una rutina de estiramientos estáticos o dinámicos

de corta duración sobre el pico de fuerza máximo y potencia media de la flexión y extensión concéntrica

y excéntrica de la rodilla.

Método: Cuarenta y nueve adultos activos completaron los siguientes protocolos de intervención en días

separados: no-estiramiento, estiramiento estático y estiramiento dinámico. Después de la intervención de

control o estiramiento, el pico de fuerza máximo y la potencia media de la flexión y extensión concéntrica

y excéntrica de la rodilla fueron medidos en posición prono. Las medidas fueron comparadas a través de

un análisis factorial ANOVA intergrupo.

∗ Corresponding author.

E-mail address: Franciscoayalarodriguez@gmail.com (F. Ayala).

http://dx.doi.org/10.1016/j.ramd.2014.06.003

1888-7546/© 2015 Consejería de Educación, Cultura y Deporte de la Junta de Andalucía. Published by Elsevier España, S.L.U. This is an open access article under the CC

BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

94 F. Ayala et al. / Rev Andal Med Deporte. 2015;8(3):93–102

Resultados: Ni el protocolo de estiramientos estático ni el dinámico tuvieron influencia sobre el pico de

fuerza máximo y potencia media isocinética cuando fueron comparados con la condición de control. Las

comparaciones por pares también mostraron que los resultados de fuerza y potencia isocinética durante

la sesión de estiramientos dinámicos fueron ligeramente mayores que los encontrados durante la sesión

de estiramientos estáticos.

Conclusiones: Una rutina de corta duración de estiramientos estáticos o dinámicos del tren inferior no

produjo alteraciones en la fuerza isocinética concéntrica y excéntrica de la flexión y extensión de rodilla.

Además, los hallazgos del presente estudio apoyan la idea de que el estiramiento dinámico podría ser

preferible antes que el estiramiento estático como parte del calentamiento previo a una actuación física.

© 2015 Consejería de Educación, Cultura y Deporte de la Junta de Andalucía. Publicado por Elsevier

España, S.L.U. Este es un artículo Open Access bajo la licencia CC BY-NC-ND

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Palavras-chave:

Aquecimento

Forc a muscular

Pico de forc a

Potência

Isocinética

Efeito agudo de 2 diferentes técnicas de alongamento sobre a forc a e potênciaisocinética

r e s u m o

Objetivos: Examinar e comparar os efeitos agudos de uma rotina de alongamentos estáticos e dinâmicos

de curta durac ão sobre o pico de forc a máxima e potência média da flexão e extensão concêntrica e

excêntrica do joelho.

Método: Quarenta e nove adultos ativos completaram os seguintes protocolos de intervenc ão em dias

distintos: sem alongamento, alongamento estático e alongamento dinâmico. Depois da intervenc ão de

alongamento ou controle, o pico de forc a máxima e a potência média da flexão, extensão concêntrica e

excêntrica do joelho foram medidos em posic ão pronada. As medidas foram comparadas através de uma

análise fatorial ANOVA intergrupo.

Resultados: Tanto o protocolo de alongamento estático quanto o protocolo de alongamento dinâmico

tiveram influência sobre o pico de forc a máxima e potência média isocinética quando comparados com a

condicão controle. As comparac ões por pares também mostraram que os resultados de forc a e potência

isocinética durante a sessão de alongamento dinâmico foram ligeiramente maiores que os encontrados

durante a sessão de alongamento estático.

Conclusão: Uma rotina de curta durac ão de alongamentos estáticos ou dinâmicos de membros inferiores

não produziram alterac ões na forc a isocinética concêntrica e excêntrica da flexão e extensão do joelho.

Além disso, os achados do presente estudo corroboram com a ideia de que alongamento dinâmico poderia

ser preferível ao invés do alongamento estático, como parte do aquecimento antes da atividade física.

© 2015 Consejería de Educación, Cultura y Deporte de la Junta de Andalucía. Publicado por Elsevier

España, S.L.U. Este é um artigo Open Access sob a licença de CC BY-NC-ND

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

Stretching activities before exercise are believed to prepare themusculo-skeletal system for physical activity and sport events byimproving joint range of motion, thus promoting improved per-formance and reducing the relative risk of injury.1 Consequently,athletes, coaches and sport practitioners regularly include stretch-ing exercises in both training programs and in pre-event warm-upactivities.2

However, recent evidence has questioned the traditionalhypothesis that supported the practice of pre-exercise stretch-ing as a measure to increase sport performance.3,4 In this sense,it has been shown that a bout of static stretching may tem-porarily reduce strength performance, in relation to force andpower production, when it is performed prior to events.3,4 It wasshown that pre-exercise static stretching might acutely compro-mise a muscle’s ability to produce strength either isometrically5,6

or isokinetically7-11(mainly under concentric actions) for theknee joint measured throughout a single-joint isokinetic test-ing protocol. Explanations for this so-called stretching-inducedstrength deficit include: (a) alterations in the mechanical compo-nents of skeletal muscle contraction7,8; (b) decreases in muscleactivation5,12,13; or (c) a combination of both mechanical and neuralfactors.7 In contrast, some evidence exists indicating that dynamicstretching exercises may induce improvement in isometric andisokinetic strength and power performance.11,14,15 Although theexact mechanisms by which dynamic stretching may improve

strength performance are not well known, previous studies havesuggested that a dynamic stretching exercise might exert posi-tive effects on muscular performance by an elevation of musculartemperature,16 or post-activation potentiation14,15caused by vo-luntary contractions of the antagonist of the target muscle.

These effects have implications for athletes involved in activitiesthat require maximal strength and power production, such as rugbyand football, and have led some researchers to recommend that pre-exercise static stretching should be omitted or replaced by dynamicstretching during warm-ups prior to strenuous exercise and/orsport events. However, when the body of literature regarding theacute effects of pre-exercise stretching on strength and power pro-duction is carefully scrutinized, some important limitations arenoted, which may question the applicability of the last recommen-dation in the physical training context. For instance, most of thestudies that have investigated the acute effects of static stretchingon strength and power have designed protocols which use overallstretch durations on a single muscle group (quadriceps, gastrocne-mius and hamstrings mainly), ranging from 90 s to 60 min.5,12-17

These single muscle group and long stretching protocols are notrepresentative of typical warm-ups used by athletes and recreat-ionally active people to prepare for exercise or competition.18 Fur-thermore, very few studies have carried out direct comparisonsbetween stretching protocols with consistent stretch doses (over-all and single stretching duration) and different stretch techniques(i.e. static vs dynamic stretching) on concentric and/or eccentricmaximal isokinetic strength and power output to elucidate the

F. Ayala et al. / Rev Andal Med Deporte. 2015;8(3):93–102 95

optimal pre-participation protocol for sport activities.11,19 Addi-tionally, although there are studies indicating improved musclestrength performance following dynamic stretching,14,15 it is notknown how dynamic stretching affects strength and power dur-ing isokinetic quadriceps and hamstring actions in concentric andeccentric modes.

Therefore, the main purpose of the current study was to examineand compare the acute effects of short duration static and dynamiclower-limb stretching routines with consistent stretching parame-ters (duration, intensity, number of exercises, repetitions) on theknee flexor and extensor peak torque and mean power duringmaximal concentric and eccentric muscle actions in recreationallyathletes.

Method

Participants

Twenty-five men (age = 21.3 ± 2.5 years; stature = 176.3 ±

8.4 cm; body mass = 74.4 ± 10.8 kg) and 24 women (age = 20.4 ± 1.8years; stature = 164.7 ± 7.6 cm; body mass = 62.9 ± 8.6 kg) whowere recreationally active adults (engaging in 2–5 h of moderatephysical activity 3–5 days per week) completed the current study.

The exclusion criteria were: (a) histories of orthopedic pro-blems, such as episodes of hamstrings and quadriceps injuries, frac-tures, surgery or pain in the spine or hamstring and quadricepsmuscles over the past six months; (b) missing a testing session dur-ing the data collection phase; and (c) not have delayed onset musclesoreness (DOMS) through each testing session. Women partici-pants could not be in the ovulation phase of their menstrual cycleduring testing to reduce the effects of hormonal status on muscle-tendon unit stiffness and knee joint laxity.20 The participants wereverbally informed about the characteristics of the methods to beutilized as well as the purpose and risks of the present study,and written informed consent was obtained from all participants.Furthermore, the study was approved by the University of Glouces-tershire Research Ethics Committee (United Kingdom).

Experimental design

A crossover study design, in which participants executed allexperimental conditions, was used to investigate the purposes ofthe current study. Use of a pre- and post-test design, in which par-ticipants performed a pre and post-stretch isokinetic assessmentwas not adopted because in a pilot study participants reported thatthe testing procedure was too long and subsequently they felt lessable to undertake the post-stretch assessment and hence, bias theresults. In addition, some participants reported musculoskeletalfatigue during the post-stretch assessment. Therefore, to ensurethe optimal preparedness state of each participant throughout thetesting procedure, the current study used a crossover design.

Participants visited the laboratory on four occasions with72–96 h rest interval between testing sessions. The first visit wasa practice/habituation session to the isokinetic testing procedureand stretching exercises, and the following three visits were theexperimental sessions. During each experimental session, partici-pants began by completing a 5 min standardized warm-up (cyclingat 90 W for men and 60 W for women at 60–70 rpm). The stretch-ing (static or dynamic) or non-stretching (control) interventionwas performed immediately after the standardized warm-up. Theorder of stretching (static and dynamic) and non-stretching con-ditions was randomized. After the stretching and non-stretchingconditions, the participants performed a specific isokinetic warm-up consisting on 4 sub-maximal (self-perceived 50% effort) and2 maximal eccentric knee flexion actions.

The rationale of using this warm up structure (standardizedwarm-up + stretching or non-stretching + specific warm-up) was toreplicate the typical warm-up structure that is usually performedby athletes and recreationally active participants.4

The knee flexor and extensor peak torque and mean powerassessment of the dominant leg (determined through interviewand defined as leg preference when kicking a ball) was carriedout 2–3 min (post-test) after the stretching protocol was com-pleted. In the non-stretching session, the knee flexor and extensorpeak torque and mean power assessment was carried out after thestandardized warm-up (Fig. 1). The rationale for assessing onlythe dominant leg was based on the fact that previous studieshave not reported leg-related differences in relation to muscle-tendon unit properties, when the same amount of stretching isapplied.21

Stretching protocols

In each stretching session, participants performed five un-assisted stretching exercises designed to stretch the major musclegroups used during running (gluteus, psoas, adductors, hamstringsand quadriceps) and reflect the stretching typically performed byathletes and recreationally active people (Fig. 2).

The static and dynamic stretching sessions differed only in thestretch technique used; whereas the other stretching load cha-racteristics (duration, intensity, repetition and exercise positions)were identical. The stretching exercises were performed twice ina randomized order under the direct supervision and guidance ofthe investigators. Each stretching exercise was completed on theright and left limb before another exercise was performed. No-restinterval was allowed between limbs, although a 20 s rest periodwas allowed between stretch repetitions and exercises (once theleg was returned to a neutral position). The intensity of stretchingwas self-determined but set to the threshold of mild discomfort,not pain, as acknowledged by the participant.

During the static stretching session, participants were asked tohold each stretch position for 30 s. During the dynamic stretch-ing session, participants were instructed to perform 15 continuouscontrolled dynamic movements from the neutral stance to the endof the range of movement. A rate of one stretch cycle every 2 s wasset and the movements were at a controlled speed throughout therange of movements. In addition, during dynamic stretching, par-ticipants were instructed that the end position should be the sameas the end position during static stretching.

Isokinetic testing

A Biodex System-3 Isokinetic dynamometer (Biodex Corp.,Shirley, NY, USA) and its respective manufacture software wereused to determine peak torque and mean power during knee exten-sion and flexion isokinetic movements.

Participants were secured in a prone position on the dynamome-ter with the hip passively flexed at 10–20◦ and the head maintainederect22 (Fig. 3). The axis of rotation of the dynamometer leverarm was aligned with the lateral epicondyle of the knee. Theforce pad was placed approximately 3 cm superior to the medialmalleolus with the foot in a relaxed position. Adjustable strap-ping across the pelvic, posterior thigh proximal to the knee andfoot localized the action of the musculature involved. The range ofmovement was set from 90◦ knee flexion (starting position) to 0◦

(0◦ was determined as maximal voluntary knee extension for eachparticipant).

The isokinetic examination was separated into two parts. Thefirst part of the examination was the assessment of the kneeextensor followed by the knee flexor muscles with a concen-tric/concentric (CON/CON) testing method. The second part of the

96 F. Ayala et al. / Rev Andal Med Deporte. 2015;8(3):93–102

Experimental sessions (k=3)

No-stretchingStatic stretching

(2 x 30 s)

Specific isokinetic warm-up

Isokinetic testing

CON/CON and ECC/ECC

Dynamic stretching

(2 x 15 rep)

72-96 h

Randomized crossover design

General warm-up

(5 min cycling)

72-96 h

1 week

Familiarization

session

49 participants

(25 males and 24 females)

Fig. 1. Flow of participants through experimental sessions of the study.

examination was the assessment of the knee extensor followedby the knee flexor muscles with an eccentric/eccentric (ECC/ECC)testing method. In both testing methods, two cycles of knee flexionsand extensions were performed at three pre-set constant angu-lar speeds in the following order: 60, 180 and 240 ◦/s (slow tofast). When a variation greater than 5% was found in the peaktorque scores between cycles at the same speed, an extra cycle wasperformed and the two most related cycles were used for the subse-quent statistical analyses. The 60 and 180 ◦/s angular speeds werechosen to be consistent with previous studies.7,8,10,23 The 240 ◦/sangular speed was chosen as the fastest velocity because in a pilotstudy with 10 participants of similar age and training status, theysubjectively indicated that 240 ◦/s was the maximum CON/CONand ECC/ECC cycles speed that they were able to perform com-fortably during the test and because the constant velocity period isvery short at velocities faster than 240 ◦/s. Pilot work also showedthat participants could not maintain the required torque outputthroughout the range of motion in the reactive eccentric mode,subsequently causing stalling of the lever arm. Therefore, the pas-sive eccentric mode was chosen so that the full range of movementwould be completed for every action.

The two testing method (CON/CON and ECC/ECC) were separateby a 5 min rest interval and a rest of 30 s was allowed betweenaction cycles. The number of maximal muscle actions and therest-period durations were chosen to minimize musculoskeletalfatigue, which is unlikely to occur with only two reciprocal muscleactions at three speeds and a 30 s rest between reciprocalmuscle actions and speeds and 5 min rest between testing modes.Both for CON/CON and ECC/ECC cycles, participants were encour-aged to push/resist as hard and as fast as possible and to completethe full range of motion.

Measures

For both isokinetic parameters of peak torque and mean power,the average of the two trials at each speed through the testingsessions was used for subsequent statistical analysis. In addition,Sole et al.24 reported better reproducibility when they used themean value from 3 trials rather than the single highest value fromthe 3 repetitions for concentric and eccentric peak torque. In eachtrial, peak torque was reported as the maximum torque value andpower was reported as time-averaged integrated area under the

Fig. 2. Stretching exercises (left to right: gluteus, quadriceps, hamstrings, psoas, and adductors).

F. Ayala et al. / Rev Andal Med Deporte. 2015;8(3):93–102 97

Fig. 3. Isokinetic testing position.

angle-torque relationship. The speed throughout each repetitionwas analyzed and it was also verified that, at the greater angularvelocity, peak torque and power was developed during the con-stant speed period. The constant speed periods during concentricmuscle actions were approximately the 82, 50 and 42% of the fullknee flexion and extension ROM for the speeds 60, 180 and 240 ◦/srespectively. For the eccentric muscle action, the constant speedperiods were 79, 48 and 40% of the full knee flexion and exten-sion ROM at 60, 180 and 240 ◦/s respectively (data obtained from20 participants).

Statistical analysis

Before any statistical analyses were performed, the distributionof raw data sets was checked using the Kolmogorov–Smirnov test.Descriptive statistics including means, standard error of the meansand 95% confidence intervals were calculated for each measure.

Recent research studies have consistently reported no sex-related differences in relation to the same stretching treatment onisokinetic peak torque values7,10,12so men’s and women’s data werenot analyzed separately. Descriptive statistics including means andstandard deviations were calculated for each measure.

Mean effects of stretching (static and dynamic) and their 90%confidence limits were estimated using a spreadsheet designedby Hopkins19 via the unequal-variances t statistic computed forchange scores between paired sessions (control vs static; control vsdynamic; static vs dynamic) for each variable. Alpha was p < 0.05.Each participant’s change score was expressed as a percentage ofbaseline score via analysis of log-transformed values, to reduce biasarising from nonuniformity of error. Errors of measurement andindividual responses expressed as coefficients of variation werealso estimated. In addition, the analysis determines the chancesthat the true effects are substantial or trivial when a value for thesmallest worthwhile change is entered.

Coefficients of variation (CV) determined the smallest substan-tial/worthwhile change for each of the variables. To the authors’knowledge, no studies have analyzed the absolute reliability of theknee flexor and extensor peak torque and mean power during ma-ximal concentric and eccentric muscle actions with the participantsadopting a prone position, so we chose 0.20 standardized units(that is a fraction of the between-subjects standard deviation atbaseline) as the smallest worthwhile change.25 The default of 0.20gives chances that the true effect is at least small.25

The qualitative descriptors proposed by Hopkins25 were used tointerpret the probabilities that the true affects are harmful, trivial

or beneficial: <1%, almost certainly not; 1–4%, very unlikely; 5–24%,unlikely or probably not; 25–74%, possibly or may be; 75–94%,likely or probably; 95–99%, very likely; >99%, almost certainly.

Effect sizes, which are standardized values that permit thedetermination of the magnitude of differences between groups orexperimental conditions,26 were also calculated for each of thevariables using the method previously described by Cohen.26

Cohen26 assigned descriptors to the effect sizes (d) such that aneffect size of 0.4 or less represented a small magnitude of changewhile 0.41–0.7 and greater than 0.7 represented moderate and largemagnitudes of change, respectively.

Results

Tables 1 and 2 present the mean and standard deviation forpeak torque and power in each experimental session (k = 3) for kneeextension and knee flexion in both concentric and eccentric muscleactions respectively.

As presented in Tables 3 and 4, there were no a clear maineffects (p > 0.05; trivial effect with a probability of 75–95%; d < 0.4)on concentric and eccentric knee flexion and extension peak torqueand power between paired treatments. However, there were pos-sible positive effects (d > 0.15; positive effect with a probability of75–95%;) of dynamic stretching on some peak torque and powervariables (see Tables 3 and 4) when they were compared with thestatic stretching treatment.

Discussion

The primary findings of the present study indicate that shortand contextualized lower limb static and dynamic stretching rou-tines have no a stretching-induce strength and power deficit orimprovement effects on concentric and eccentric knee flexion andextension isokinetic movements at three different speeds (60, 180and 240 ◦/s) in recreationally athletes.

Our findings are not consistent with several recentstudies,11,12,17-27 although not all,23,28,29 that has indicated that about of static stretching may cause transient decreases in isolatedmuscle strength. A possible explanation for these conflictingresults could be attributed to the different static stretch dura-tions used in these studies. Generally, in those studies that havereported static stretching-induced strength and power deficits,a single muscle group was statically stretched for between 90 sand 60 min.5,12-17 Contrarily, our study in conjunction with somestudies that have shown no static stretching-induced strengthand power deficits have used a lower overall stretch durationranging from 30 to 90 s.23,28,29 Therefore, it would appear thatthere is a dose-dependent threshold of static stretching necessaryto reflect any statistically detectable change in isokinetic strengthand power. This hypothesis has been recently confirmed by somestudies which have examined and carried out direct comparisonsbetween the acute effects of stretching routines with differentoverall stretch doses and consistent stretching parameters (tech-nique intensity, exercise positions and muscle stretched).23,28,30–32

For example, Zakas et al.23 after examining the effects of two dif-ferent overall durations (45 s and 300 s) of acute static stretchingon isokinetic peak torque production in pubescent soccer playersreported that stretching caused a significant decrease in strengthperformance (5–12%) when the stretch duration was 300 s, whilea stretch duration per isolate muscle of 45 s did not alter themechanism of force production. In addition, Murphy et al.30 foundthat a bout of 6 × 6 s of static stretching for the hamstring wasenough to improve hip flexion ROM for 30 minutes without causeimpairments on jump height and reaction time. Consequently,overall static stretch duration per isolate muscle group ≤60–90 s

98 F. Ayala et al. / Rev Andal Med Deporte. 2015;8(3):93–102

Table 1Peak torque and mean power output among experimental sessions (k = 3) during concentric and eccentric knee extension muscle actions.a

Concentric mode Eccentric mode

60 ◦/s 180 ◦/s 240 ◦/s 60 ◦/s 180 ◦/s 240 ◦/s

No-stretching session (control)

Peak torque (Nm) 120.7 ± 33.7 96.7 ± 34.7 92.6 ± 29.2 169.5 ± 66.5 148.0 ± 38.7 144.4 ± 49.7

Power (W) 60.4 ± 18.5 99.2 ± 35.8 99.2 ± 35.8 81.00 ± 32.1 140.0 ± 40.9 172.5 ± 48.7

Static stretching session

Peak torque (Nm) 122.4 ± 36.7 95.1 ± 30.1 88.4 ± 29.0 154.9 ± 67.8 142.4 ± 40.5 143.2 ± 58.4

Power (W) 63.4 ± 18.5 95.8 ± 32.3 101.3 ± 36.6 78.0 ± 28.0 133.1 ± 42.1 174.5 ± 52.0

Dynamic stretching session

Peak torque (Nm) 128.4 ± 41.7 98.7 ± 29.9 91.5 ± 31.5 165.1 ± 64.5 160.5 ± 63.1 147.6 ± 53.0

Power (W) 64.5 ± 21.9 100.3 ± 33.0 99.9 ± 38.0 79.3 ± 35.6 141.5 ± 41.0 172.1 ± 53.6

a All values are mean ± standard deviation.

Table 2Peak torque and mean power output among experimental sessions (k = 3) during concentric and eccentric knee flexion muscle actions.a

Concentric mode Eccentric mode

60 ◦/s 180 ◦/s 240 ◦/s 60 ◦/s 180 ◦/s 240 ◦/s

No-stretching session (control)

Peak torque (Nm) 74.7 ± 24.7 68.1 ± 23.2 64.0 ± 22.8 82.6 ± 27.7 83.1 ± 26.2 80.6 ± 25.8

Power (W) 45.5 ± 13.7 78.3 ± 23.8 81.2 ± 28.9 48.3 ± 18.6 80.1 ± 38.8 92.4 ± 33.6

Static stretching session

Peak torque (Nm) 72.8 ± 24.1 65.7 ± 21.7 57.8 ± 20.8 83.5 ± 25.5 79.6 ± 23.3 78.5 ± 23.7

Power (W) 44.5 ± 14.2 77.7 ± 24.9 76.0 ± 26.5 50.1 ± 16.6 76.6 ± 41.9 89.5 ± 32.7

Dynamic stretching session

Peak torque (Nm) 75.0 ± 22.6 69.6 ± 21.3 60.9 ± 22.9 84.7 ± 28.6 81.8 ± 23.9 77.6 ± 26.9

Power (W) 46.4 ± 13.9 80.3 ± 23.4 83.6 ± 26.7 49.8 ± 17.4 82.3 ± 39.0 90.3 ± 34.5

a All values are mean ± standard deviation.

may have no stretching-induced alterations in strength and powerduring concentric and eccentric isokinetic muscle actions.

The results of the current study also suggest that therewere no significant differences in isokinetic strength and powerperformance after dynamic stretching compared with controlcondition. These findings are not consistent with previous stud-ies that have reported increased strength and/or power after about of dynamic stretching.11,33,34 A possible explanation for thediscrepancy between the results of the current study, thatshowed no dynamic stretching-induced improvements on isoki-netic strength and power; in contrast with the results reportedby previous studies may be due to the different stretch durationused. For example, Sekir et al.11 designed a dynamic stretchingprotocol with an overall stretch duration per muscle (quadricepsand hamstrings) of 60 s (4 × 15 dynamic movements) and Manoelet al.34 carried out 3 repetitions of 30 s dynamic stretches, whilethe current study stretched the major muscle groups of the lowerlimb (psoas, quadriceps, hamstrings, gluteus and adductors) usinga overall stretch duration of 30 s per muscle group (2 × 15 dynamicmovements). Perhaps, as occur with static stretching, the dynamicstretching-induced enhancement of muscular performance phe-nomenon may be governed by a dose–response relationship, wherethe shorter volumes (<30 s) do not affect muscle performance andlonger duration may facilitate performance (>60–90 s).4 However,future studies are necessary to test this hypothesis.

Another important issue regarding the pre-exercise stretch-ing routine design is the stretch technique used. When static anddynamic stretching treatments were compared, the results of thecurrent study showed that dynamic stretching reported slightlyhigher scores than static stretching (d > 0.15; percentage changeranged form 1.2 to 14.7) for most of the strength and powervariables. Therefore, this finding supports the recent claims thatsuggest that dynamic stretching is preferable to static stretchingas part of a warm-up designed to prepare for physical activity

due to the possible enhancement of muscular performance11,33–37;and the similar acute increases in static flexibility as staticstretching.38,39

Another important clinical question is whether the effects ofstretching of knee flexor and extensor muscle groups, which areclosely related to the actual demands of sport on strength perfor-mance, elicit a similar response, in order to make evidence-basedrecommendations. The results of the current study and the findingsreported by Sekir et al.11 have demonstrated that knee flexor andextensor muscles respond in the same way to static and dynamicstretching.

Two different methodological aspects of the current studyshould be highlighted because they might make the results morevalid than previous studies. The first aspect is the design ofthe stretching protocol used. The current study used a multiple-muscle stretching protocol (in which participants stretched themajor lower-limb muscles) instead of the widely used single-muscle protocol (in which participants stretched only the musclestudied).15-27 The rationale for using a multiple-muscle stretch-ing protocol was because an acute bout of static stretching mayreduce muscle activation via peripheral (autogenic inhibition ofthe Golgi tendon reflex, mechanoreceptor and nociceptor affer-ent inhibition) and central nervous system (supraspinal fatigue)mechanisms.5,8,12 In this sense, Avela et al.5 and Cramer et al.8

found that an acute bout of static stretching caused a decreasein muscle activation not only in the stretched muscle but also inthe un-stretched contralateral muscle (via central nervous sys-tem mechanism). However, the degree of contribution of eachmechanism (peripheral and central) on the reduction in muscleactivation is still unclear. Therefore, effects of stretching beforeexercise and sport events should be investigated using multiple-muscle stretching protocols that reflect the stretching stimuli thatathletes and recreationally active people usually apply both to theperipheral and central nervous system during a typical warm-up

F.

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Table 3Concentric (CON) and eccentric (ECC) knee flexion peak torque (PT) and power (PW) percentage changes (mean, 90% confidence limit), effect size (d) and likelihood (%) of being positive/trivial/negative among treatment sessions

(paired comparisons). Practical assessments of the effects are also shown.a

Static vs control Dynamic vs control Dynamic vs static

Change (%) Effect size Change (%) Effect size Change (%) Effect size

+/Trivial/− (inference) +/Trivial/− (inference) +/Trivial/− (inference)

PTCON60−3.1 (−8.5 to 2.7) −0.09 0.9 (−3.5 to 5.5) 0.03 4.8 (−1.3 to 11.2) 0.14

1/76/23 (likely trivial) 6/92/2 (likely trivial) 45/54/0 (possible positive)

PTCON180−2.8 (−8.4 to 3.2) −0.08 1.5 (−3.9 to 7.2 0.04 5.5 (−0.5 to 11.9) 0.15

0/87/13 (likely trivial) 5/94/1 (likely trivial) 32/68/0 (possible positive)

PTCON240−9.4 (−15.7 to −2.7) −0.27 −3.8 (−9.6 to 2.2 −0.11 6.4 (−1.7 to 15.1) 0.17

0/26/74 (possible negative) 0/81/19 (likely trivial) 41/58/0 (possible positive)

PWCON60−4.5 (−10.0 to 1.3) −0.14 1.4 (−4.2 to 7.4) 0.04 6.7 (0.1 to 13.7) 0.19

1/64/55 (possible trivial) 21/74/5 (possible trivial) 72/28/0 (possible positive)

PWCON180−0.1 (−5.9 to 6.0) 0.01 0.6 (−3.8 to 5.1) 0.02 1.2 (−6.2 to 9.1) 0.04

3/93/4 (likely trivial) 2/98/0 (very likely trivial) 11/84/4 (likely trivial)

PWCON240−6.2 (−14.5 to 3.0) −0.17 −0.5 (−5.8 to 5.1) 0.02 7.1 (−3.3 to 11.1) 0.18

1/58/42 (possible negative) 1/97/2 (very likely trivial) 45/53/2 (possible positive)

PTECC60−0.8 (−4.9 to 3.5) −0.02 2.6 (−1.6 to 6.9) 0.07 4.0 (0.1 to 8.2) 0.11

0/99/1 (very likely trivial) 5/95/0 (very likely trivial) 11/84/0 (likely trivial)

PTECC180−4.7 (−9.7 to 0.6) −0.15 −0.4 (−4.3 to 3.8) −0.01 5.3 (−0.3 to 11.1) 0.16

0/70/30 (possible trivial) 0/99/1 (very likely trivial) 35/65/0 (possible positive)

PTECC240−3.0 (−7.6 to 1.9) −0.09 −1.4 (−5.6 to 3.0) −0.04 1.8 (−3.5 to 7.5) 0.06

0/88/12 (likely trivial) 0/97/3 (very likely trivial) 8/92/1 (likely trivial)

PWECC603.8 (−2.7 to 10.6) 0.09 4.1 (−2.1 to 10.6) 0.1 2.6 (−3.1 to 8.6) 0.06

14/86/0 (likely trivial) 14/86/0 (likely trivial) 6/94/0 (likely trivial)

PWECC180−4.2 (−11.3 to 3.6) −0.12 3.2 (−2.6 to 9.3) 0.09 8.8 (0.6 to 17.6) 0.24

1/76/23 (likely trivial) 15/85/0 (likely trivial) 64/36/0 possible positive)

PWECC240−4.0 (−10.3 to 2.8) −0.11 −0.3 (−6.1 to 5.9) −0.01 2.8 (−4.0 to 10.1) 0.08

0/79/21 (likely trivial) 2/96/3 (very likely trivial) 13/86/1 (likely trivial)

a If chance of benefit and harm both >5%, true effect was assessed as unclear (could be beneficial or harmful). Otherwise, chances of benefit or harm were assessed as follows: <1%, almost certainly not; 1–5%, very unlikely;

>5–25%, unlikely; >25–75%, possible; >75–95%, likely; >95–99%, very likely; >99%, almost certain.

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Table 4Concentric (CON) and eccentric (ECC) knee extension peak torque (PT) and power (PW) percentage changes (mean, 90% confidence limit), effect size (d) and likelihood (%) of being positive/trivial/negative among treatment

sessions (paired comparisons). Practical assessments of the effects are also shown.a

Static vs control Dynamic vs control Dynamic vs static

Change (%) Effect size Change (%) Effect size Change (%) Effect size

+/Trivial/− (inference) +/Trivial/− (inference) +/Trivial/− (inference)

PTCON600.2 (−5.6 to 6.3) 0.01 4.2 (−1.5 to 10.2) 0.14 4.3 (−4.2 to 13.5) 0.14

9/84/7 (likely trivial) 39/61/0 (possible positive) 43/53/4 (possible positive)

PTCON1800.9 (−8.3 to 7.2) −0.03 0.5 (−6.7 to 8.4) 0.02 3.8 (−3.0 to 11.0) 0.11

5/85/10 (likely trivial) 8/87/5 (likely trivial) 21/78/1 (likely trivial)

PTCON240−7.8 (−14.4 to −0.8) −0.25 −0.8 (−5.6 to 4.2) −0.03 7.3 (−0.9 to 16.2) 0.22

0/36/64 (possible negative) 1/96/3 (very likely trivial) 54/45/0 (possible positive)

PWCON600.6 (−5.6 to 7.1) 0.02 1.7 (−4.7 to 8.5) 0.05 1.6 (−6.7 to 10.6) 0.05

14/71/9 (likely trivial) 22/72/6 (possible trivial) 28/61/11 (possible trivial)

PWCON180−2.9 (−9.8 to 4.5) −0.08 −0.7 (−7.8 to 6.9) −0.02 6.1 (−1.5 to 14.3) 0.16

1/82/17 (likely trivial) 4/89/7 (likely trivial) 38/62/0 (possible positive

PWCON240−3.3 (−11.2 to 5.3) −0.10 −2.4 (−8.5 to 4.2) −0.07 2.0 (−7.6 to 12.5) 0.06

2/74/23 (likely trivial) 1/87/12 (likely trivial) 19/74/7 (possible trivial)

PTECC60−5.9 (−12.5 to 1.1) −0.16 −3.5 (−9.4 to 2.8) −0.09 5.1 (−2.3 to 13.1) 0.13

0/56/44 (possible negative) 0/79/20 (likely trivial) 34/65/1 (possible positive)

PTECC180−4.5 (−12.6 to 4.3) −0.13 9.0 (−4.0 to 23.7) 0.25 14.7 (0.6 to 30.9) 0.40

1/70/29 (possible trivial) 59/38/2 (possible positive) 81/18/1 (likely positive)

PTECC240−5.4 (−17.7 to 8.8) −0.12 −1.9 (−9.5 to 6.4) −0.04 −2.5 (−9.1 to 4.5) −0.06

4/67/29 (possible trivial) 1/92/7 (likely trivial) 0/94/6 (likely trivial)

PWECC60−3.2 (−9.9 to 4.0) −0.08 −3.1 (−9.8 to 4.0) −0.08 2.4 (−5.8 to 11.4) 0.06

1/84/15 (likely trivial) 0/85/15 (likely trivial) 15/83/2 (likely trivial)

PWECC180−6.0 (−14.4 to 3.3) −0.17 2.0 (−5.8 to 10.5) 0.06 9.4 (2.1 to 17.3) 0.25

1/55/44 (possible negative) 15/82/3 (likely trivial) 68/32/0 (possible positive)

PWECC2403.8 (−4.9 to 13.4) 0.10 −0.6 (−9.3 to 11.6) 0.02 −1.6 (−8.6 to 5.9) −0.04

16/82/2 (likely trivial) 5/85/11 (likely trivial) 3/87/10 (likely trivial)

a If chance of benefit and harm both >5%, true effect was assessed as unclear (could be beneficial or harmful). Otherwise, chances of benefit or harm were assessed as follows: <1%, almost certainly not; 1–4%, very unlikely;

5–24%, unlikely; 25–74%, possible; 75–94%, likely; 95–99%, very likely; >99%, almost certain.

F. Ayala et al. / Rev Andal Med Deporte. 2015;8(3):93–102 101

to make evidence-based recommendations. The second methodo-logical aspect that should be underlined is related to the isokinetictesting position used. Studies that have investigated the effectsof stretching on isokinetic strength, with the goal of making re-commendations to design warm-up protocols that allow athletesimproving performance and reducing the risk of lower limb muscu-loskeletal injury, have typically reported data obtained from par-ticipants tested in a seated position. However, rarely are field andcourt sport athletes active with those kinematics (e.g., the hip flexedat 80–110◦).40,41 Most lower limb injuries occur while athletesengage in some running activity where the hip angle is reportedto typically be approximately 10–20◦ to the vertical with footplant occurring directly inferior to the torso and not with a hipflexion angle of 80–110◦.41 Thus, it could be argued that isoki-netic screening where the hip angle is more similar to whenexecuting real-world sporting tasks would be more ecologicallyvalid than using other traditional methods.22,40 Based on the laststatement, the current study selected a prone position with hipflexed 10–20◦, which replicates the hip position and knee flexorand extensor muscle length-tension relationships that occur dur-ing running/sprinting.22,40 Although the standing position appearsto be the most ecologic valid testing position, it was not usedbecause of technical issues (the bench of the dynamometer couldnot adapted to this position). However, it is possible that if the samehip flexion is used in both standing and prone positions, the stretch-tension relationship of the knee flexors and extensors will not likelydiffer and the relative contribution of the active contractile compo-nents of the muscles to overall force production would not change.Future studies are necessary to test this hypothesis.

Although the current study is the first that has designed andexamined the acute effects of a short and sport contextualizedstatic and dynamic pre-exercise lower limb stretching routine withconsistent stretch parameters on several isokinetic concentric andeccentric strength parameters (peak torque and power) in a largesample size of recreationally athletes, some limitations should benoted. The first limitation is that this study did not directly ev-aluate changes in the range of motion or changes in resistance andtolerance to stretch due to the experimental stretching treatments.Therefore it is not known whether the stretching interventionswere actually effective in increasing flexibility or in decreasingmuscle stiffness, although previous studies from our laboratorythat have used identical stretching doses have reported increasesin flexibility.38 Another potential limitation of the current study isthe population used. Although this investigation used 49 partici-pants, much higher than previous studies, the participants werehomogenous based on age and physical status, which could limitthe external validity of the results.

Therefore, the results of the present study indicate that shortpre-exercise static and dynamic lower-limb stretching routines donot elicit stretching-induce deficits or improvements on knee flexorand knee extensor isokinetic concentric and eccentric strength andpower. However, there is some evidence from our findings, in con-junction with similar previous studies, that dynamic stretching ispreferable to static stretching as part of a warm-up designed toprepare for physical activity due to the possible enhancement ofmuscular performance.

Conflicts of interest

The authors have no conflicts of interest to declare.

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